Study of EPR zero-field splitting of iron–sulfur clusters in tetrahedral ZnS:FeIII system ☆

Abstract The EPR zero-field splitting of the iron–sulfur cluster in the ZnS:Fe III system has been studied on the basis of the energy matrix for the electron–electron repulsion, the ligand–field and the spin–orbit coupling of a d 5 configuration ion with a trigonal symmetry. It is demonstrated that in order to reasonably explain the EPR zero-field splitting parameters a, D and ( a − F ), a positive ligand–field strength Dq for a d 5 electron configuration ion in a tetrahedron has to be employed. This means that the effective charge of each sulfur ion in ZnS is positive. This unusual result leads to the conclusion that in ZnS each sulfur ion may occur a quadricovalent argon state S 2+ with sp 3 hybrid configuration and this conclusion is in accord with Pauling's speculation.